During the 19th century, some famous scientists and health care workers including Florence Nightingale believed that filth in itself caused diseases. We now know that it is not filth and dirt in themselves that cause disease; it is the bacteria that thrive in unsanitary and unclean conditions.
Bacteria are very tiny forms of life visible only under a microscope. To give you a rough idea of their size, imagine all eight million people reduced to the size of bacteria. They would fit very comfortably into a drop of water!
When scientists had the microscope, knowledge about bacteria increased and one after another of the bacteria causing diseases were discovered and investigated. The bacillus of tuberculosis was discovered in 1882; the bacillus of diphtheria and that of tetanus in 1884. Today, most of the diseases caused by bacteria are understood.
- Single-celled microorganisms
- Most can reproduce outside the host cells, and oxygen requirements dictate where the bacteria can best survive:
- Aerobic: bacteria that require oxygen for growth
- Anaerobic: bacteria that do not require oxygen for growth, survive best in deep tissues of the body where oxygen supply is limited- This type of bacterial infection is difficult to treat because antimicrobial drugs often travel within the vascular system to affect local tissues. The deeper tissues are much more difficult to penetrate.
- Some bacteria can survive in both aerobic and anaerobic environments.
- Bacteria are often referred to by their shape:
- Cocci (spheres) – round cells that include streptococci and staphylococci
- Bacilli (rods) – rod-shaped cells that include tetanus and TB
- Vibrio (Comma-shaped) – curved rods – Vibrio bacteria – one of which causes cholera
- Spirochetes (spirals)
- Bacteria structure:
- indiscrete nucleus -bacteria have no nuclear membrane therefore not separate from the cytoplasm
- cell membrane
- Most bacteria have a rigid cell wall that surrounds the cell membrane to provides shape and structure. Because human cells do not have a cell wall, antibiotic treatment is commonly aimed at inhibiting the synthesis of the bacterial cell wall during bacterial replication.
- Some bacteria have a capsule covering the cell wall, making it easily adhere to host cells. The capsule is highly resistant to phagocytosis.
- Therefore, the cell wall and capsule is important in the pathogenicity of the bacteria and will often direct treatment decisions.
- Structural properties critical to the pathogenicity of bacteria:
- Independent survival – Bacteria the can survive outside the human host, can infect and re-infect if not destroyed.
- Stimulation of an inflammatory response – Bacteria stimulate an inflammatory and immune response that will destroy surrounding host tissues to rid the body of the invader.
- Bacterial capsule – Encapsulated bacteria are adherent and highly resistant to phagocytosis
- Endotoxin – The presence of endotoxin in the gram-negative bacterial cell envelope activates the plasma protein systems. It causes inflammatory mediators to be released, leading to a massive inflammatory response. This in turn can result in a state of septic shock accompanied by severe diarrhea, fever, and leukocytosis. When inducing fever, these endotoxin-containing bacteria are referred to as pyogenic bacteria
- Endospores – Bacteria can produce spores that survive in a latent state that is resistant to environmental extremes and lack of nutrients. When the environment is more conducive to replication, the bacteria will emerge from the spore state, multiple, and may cause infection in a susceptible host.
Luckily, most bacteria, which are all around us, are more beneficial than harmful to mankind. For example, resident flora – microorganisms that live on or within the body in nonsterile areas, such as the skin, mucous membranes, bowel, rectum, or vagina, without causing harm. Bacteria are very important in destroying dead matter. You might say that they are our most efficient department for garbage disposal. Bacteria help the growth of certain plants on which all other plants and animal depend. In fact, life without bacteria would not be possible, yet how pleasant it would be without the bacteria that cause TB, pneumonia, syphilis, and diphtheria, to name just a few!